The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent that it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Direct conversion transmitters are commonly utilized in phase-modulated wireless transmission systems. In direct conversion, the signal to be transmitted is directly generated at radio frequency through a combination of I and Q paths. The resulting signal is then amplified by a linear power amplifier and transmitted. One alternative to the direct conversion transmitter is the polar transmitter. In a polar transmitter, the signal to be transmitted is generated based on a phase signal and an amplitude signal, which is then amplified by a non-linear amplifier. Because non-linear amplifiers can be more efficient than linear amplifiers, polar transmitters can be more efficient than direct conversion transmitters. But when the trajectory of the signal to be transmitted crosses near or at the origin of the complex plane, the abrupt variation in the output phase that results causes a frequency spike in a polar transmitter. The drawback to a conventional polar transmitter is therefore that it requires wide-band amplitude and wide-band phase modulation, which are not easy to achieve and result in high power consumption.
Zero Crossing Avoidance is a technique that alters the trajectory of the signal to be transmitted such that the signal avoids passing near to the origin of the complex plane. This technique results in less of a frequency spike because the trajectory avoids the origin, and the phase and the frequency of the resulting signal has a smoother transition.